There is a detection device formed of an electromagnetic conversion element and a magnet as a device magnetically detecting a movement of a magnetic movable body. The electromagnetic conversion element referred to herein means an element having an electrical resistance value that varies with an applied field, such as an MR (Magneto-Resistance) element. Because a field applied to the electromagnetic conversion element varies with a movement of the magnetic movable body, the movement of the magnetic movable body can be detected as a variance of the electrical resistance value.
For example, a field sensor of PTL 1 discloses a spin-valve MR element as the electromagnetic conversion element. The spin-valve MR element has ferromagnetic first and second thin-film layers separated by a non-magnetic thin-film layer. A magnetization direction of the ferromagnetic second thin-film layer is fixed (magnetization fixed layer). The magnetization is fixed by means of bringing an antiferromagnetic thin-film layer (pinning layer) into direct contact with the magnetization fixed layer. Meanwhile, a magnetization direction of the ferromagnetic first thin-film layer varies freely with an applied field (magnetization free layer).
In comparison with an AMR (Anisotropic Magneto-Resistance) element as a typical MR element, the spin-valve MR element has a large variance of the electrical resistance value (a magneto-resistance change rate, namely, an MR ratio) and therefore highly sensitive detection is made possible. The spin-valve MR element includes a GMR (Giant Magneto-Resistance) element and a TMR (tunneling Magneto-Resistance) element. In particular, the TMR element is receiving attention recently because of its large MR ratio.
FIG. 20 shows a variance of an electrical resistance value of a spin-valve MR element 3. The electrical resistance value of the spin-valve MR element 3 varies with an angle yielded between a magnetization direction of a magnetization fixed layer 3b and a magnetization direction of a magnetization free layer 3a. Hence, when a direction of a field applied to the spin-valve MR element 3 rotates, a variance of the electrical resistance value of the spin-valve MR element 3 appears in the form of a cosine wave or a sine wave.
FIGS. 21A and 21B are configuration views showing an example of a magnetic position detection device in the related art. An operating principle underlying one example of the magnetic position detection device using spin-valve MR elements 3 as shown in FIGS. 21A and 21B will now be described. A magnetic movable body 10 is magnetized so that N-poles and S-poles alternately appear and has a region in which distances between the N-poles and the S-poles are constant. The spin-valve MR elements 3 are located in a region A and a region B of field detection portions 2 a distance d away from the magnetic movable body 10. A distance between the regions A and B is given as λ/2 with respect to a magnetization pitch (distance between an N-pole and another N-pole) λ of the magnetic movable body 10. Also, field detection portions Ra1 and Ra2 are located in the region A and field detection portions Rb1 and Rb2 are located in the region B. The field detection portions Ra1, Ra2, Rb1, and Rb2 are set so that magnetization directions of the magnetization fixed layers 3b of the spin-valve MR elements 3 forming the respective field detection portions are all in a same direction with respect to a movement direction of the magnetic movable body 10 and connected so as to form a bridge circuit 20 as is shown in FIG. 22.
When a direction of the field applied to the spin-valve MR elements 3 rotates in association with a movement (rotation) of the magnetic movable body 10, the electrical resistance values of the spin-valve MR elements 3 vary as is shown in FIG. 20. Hence, a differential output Vout of the bridge circuit 20 of the device shown in FIG. 22 forms a waveform close to a cosine wave or a sine wave as is shown in FIG. 23. A movement distance s (rotational angle β) of the magnetic movable body 10 can be calculated on the assumption that a differential output Vout of the bridge circuit forms a cosine wave or a sine wave. Referring to FIG. 22, numeral 40 is a detection circuit, numeral 41 is a differential amplifier circuit, and numeral 42 is a signal processing circuit.